1. Field of the Invention
The present invention relates to a switching mode power supply, and in particular to a switching mode power supply having an Energy Based Pulsed Generator.
2. The Prior Arts
In recent technology development, DC to DC converters have become one of the widely used power supplies, and can be divided into three types of Buck converters, Boost converters, and Buck-Boost converters due to their different voltage-modulating characteristics. Therefore, three different circuit implementations, including Low-Dropout Linear Regulator, Switching Mode Power Supply, and Switching Capacitor Power Supply, which is respectively carried out by the buck converter, boost converter, and buck-Boost converter, are commonly required in many types of portable devices for extending the battery life.
To be more specific, the Low-Dropout Linear Regulator has lower power transfer efficiency and can only be applied to buck converters, thereby limiting its application range. On the other hand, the Switching Mode Power Supply and the Switching Capacitor Power Supply can be both applied to buck and boost converters, or to output opposite voltage according to different topology. Therefore, compared to the Low-Dropout Linear Regulator, the Switching Mode Power Supply is considered to be having higher power transfer efficiency, wider load range, capable of effectively modulating output voltages, and thus being widely used in many types of electronics products.
In general, there are many different operating modes for users to switch the converter due to different applications. For example, these modes may include normal mode, efficient mode, sleep mode, and etc. A switch between these different modes usually induces the loading current of the DC to DC converter to be changed. As mentioned before, the above mentioned converters are set to provide different loading current according to different operating modes, or how heavy or light the load condition is. Also, the converters have to keep high power transfer efficiency even under an extremely wide load range, and to respond to how the load condition or input energy changes in a short time, to aim for a proper output voltage range.
However, the power transfer efficiency of converters is usually related to its load condition. For example, in bulk converter designs, power losses come mainly from conduction losses with a heavy load while switching losses dominate with a light load. As a result, to improve power transfer efficiency over a wide load range, converters in the conventional way usually hop alternatively between PWM (Pulse-Width Modulation) mode and PFM (Pulse Frequency Modulation) mode for heavy and light load conditions, respectively.
FIG. 1 illustrates a conventional circuit diagram of control mode hopping technology, which uses a control mode detection unit 2 and a control mode selecting unit 3 for detecting the load condition of a power stage 4, feeding the result back to a multi-mode controller 1 for switching to a proper control mode, and eventually driving the power stage 4 through a power transistor buffer 5. However, it should be noted that, not only does the converter require different control blocks (including the Pulse width modulation, PWM 11 and the Pulse frequency modulation, PFM 12), the mode decision circuits should also be developed to precisely change the operation mode. As a result, the converter is complicated and incurs significant voltage variation during changes in the operation mode. Furthermore, a larger voltage ripple is induced in PFM mode because a large enough peak inductor current is set to improve the power transfer efficiency.
Therefore, the persons skilled in the art are eager to develop a novel switching mode power supply with a more simple control circuit that effectively adjust and switch the converter so as to overcome the above-mentioned problems.